Brexit: Theresa May says deal will 'safeguard progress' in NI
The prime minister says her Brexit deal will safeguard "hard won progress" in Northern Ireland.
Theresa May was speaking after EU leaders approved the deal at a summit in Brussels.
The Taoiseach (Irish prime minister) said the deal was the "next best outcome" to the UK staying in the EU and joined other EU leaders in warning that it will not be renegotiated.
However, Leo Varadkar said he continues to regret the UK's EU departure.
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'There is no Plan B'
Mrs May insisted it is the "best and only deal possible".
She said it meant she had kept a 'solemn commitment' that there would be no hard border in Ireland.
Mrs May added that the deal meant people in Northern Ireland can "carry on living their lives as they do today".
Mr Varadkar said there "isn't a Plan B".
"What we have here is the best deal available for the UK and the EU," he said.
He said those who were suggesting a better deal was available could not even agree what that deal was.
"Anyone can have a better deal or alternative deal in their own minds," said Mr Varadkar.
"What's on the table is the only deal that's on the table."
'A very difficult deal'
The 27 leaders approved the deal at a special EU summit in the Belgian capital on Sunday.
They also backed a declaration on the future UK-EU relationship.
However, Mrs May faces a struggle to get the deal approved by the UK parliament.
Earlier, Mr Varadkar said it had been a "very difficult" deal to negotiate, but it will allow the UK to leave in an "orderly way".
"The best outcome for Ireland and for Europe and Britain would be for the UK to stay in the EU and stay in the single market and the customs union, but we respect their decision not to do that," Mr Varadkar said.
"We have an agreement that allows for an orderly withdrawal."
Donald Tusk made the remark in a letter to EU leaders ahead of the summit.
Mr Tusk, who chairs the group of EU national leaders, said the deal means the peace process in Northern Ireland "should not be affected".
He added: "During these negotiations, no-one wanted to defeat anyone."
The prime minister said her agreement promises a "brighter future" for the UK and leaving the EU next year will be "a moment of renewal and reconciliation for our whole country".
Mr Tusk has recommended all countries approve the agreement.
'Junk the backstop'
Spain - which had threatened to boycott the summit - will attend after a last-minute disagreement over Gibraltar was resolved on Saturday.
However, even if the EU agrees to the deal, it needs to be passed by the UK Parliament.
Many MPs - including in Mrs May's own Conservative Party - have stated they will vote against it.
He told the DUP conference the EU had made Northern Ireland an "indispensable bargaining chip" in the Brexit negotiations.
DUP leader Arlene Foster said a Brexit deal that includes the backstop plan is "not in the national interest".
There has been political opposition among unionists to the government's plan because of the backstop, which aims to avoid a hard Irish border.
It would see only Northern Ireland stay aligned to some EU rules if it took effect.